Enlarge / A photo of Braarudosphaera bigelowii with the nitroplast indicated by an arrowhead. (credit: Tyler Coale )

The complex cells that underlie animals and plants have a large collection of what are called organelles—compartments surrounded by membranes that perform specialized functions. Two of these were formed through a process called endosymbiosis, in which a once free-living organism is incorporated into a cell. These are the mitochondrion, where a former bacteria now handles the task of converting chemical energy into useful forms, and the chloroplast, where photosynthesis happens.

The fact that there are only a few cases of organelles that evolved through endosymbiosis suggests that it's an extremely rare event. Yet researchers may have found a new case, in which an organelle devoted to fixing nitrogen from the atmosphere is in the process of evolving. The resulting organelle, termed a nitroplast, is still in the process of specialization.

Getting nitrogen

Nitrogen is one of the elements central to life. Every DNA base, every amino acid in a protein contains at least one, and often several, nitrogen atoms. But nitrogen is remarkably difficult for life to get ahold of. N ₂ molecules might be extremely abundant in our atmosphere, but they're extremely difficult to break apart. The enzymes that can, called nitrogenases, are only found in bacteria, and they don't work in the presence of oxygen. Other organisms have to get nitrogen from their environment, which is one of the reasons we use so much energy to supply nitrogen fertilizers to many crops.

Enlarge / The plague bacteria, Yersina pestis , is a close relative of the toxin-producing species studied here. (credit: Callista Images )

Life-forms with no brain are capable of some astounding things. It might sound like sci-fi nightmare fuel, but some bacteria can wage kamikaze chemical warfare.

Pathogenic bacteria make us sick by secreting toxins. While the release of smaller toxin molecules is well understood, methods of releasing larger toxin molecules have mostly eluded us until now. Researcher Stefan Raunser, director of the Max Planck Institute of Molecular Physiology, and his team finally found out how the insect pathogen Yersinia entomophaga (which attacks beetles) releases its large-molecule toxin.

They found that designated “soldier cells” sacrifice themselves and explode to deploy the poison inside their victim. “YenTc appears to be the first example of an anti-eukaryotic toxin using this newly established type of secretion system,” the researchers said in a study recently published in Nature.

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What if human blood turned into a sort of rubbery slime that can bounce back into a wound and stop it from bleeding in record time?

Until now, it was a mystery how hemolymph, or insect blood, was able to clot so quickly outside the body. Researchers from Clemson University have finally figured out how this works through observing caterpillars and cockroaches. By changing its physical properties, the blood of these animals can seal wounds in about a minute because the watery hemolymph that initially bleeds out turns into a viscoelastic substance outside of the body and retracts back to the wound.

“In insects vulnerable to dehydration, the mechanistic reaction of blood after wounding is rapid,” the research team said in a study recently published in Frontiers in Soft Matter. “It allows insects to minimize blood loss by sealing the wound and forming primary clots that provide scaffolding for the formation of new tissue.”

Enlarge / Active geology could have helped purify key chemicals needed for life. (credit: Christof B. Mast)

In some ways, the origin of life is looking much less mystifying than it was a few decades ago. Researchers have figured out how some of the fundamental molecules needed for life can form via reactions that start with extremely simple chemicals that were likely to have been present on the early Earth. (We've covered at least one of many examples of this sort of work.)

But that research has led to somewhat subtler but no less challenging questions. While these reactions will form key components of DNA and protein, those are often just one part of a complicated mix of reaction products. And often, to get something truly biologically relevant, they'll have to react with some other molecules, each of which is part of its own complicated mix of reaction products. By the time these are all brought together, the key molecules may only represent a tiny fraction of the total list of chemicals present.

So, forming a more life-like chemistry still seems like a challenge. But a group of German chemists is now suggesting that the Earth itself provides a solution. Warm fluids moving through tiny fissures in rocks can potentially separate out mixes of chemicals, enriching some individual chemicals by three orders of magnitude.

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When we talk about memories in biology, we tend to focus on the brain and the storage of information in neurons. But there are lots of other memories that persist within our cells. Cells remember their developmental history, whether they've been exposed to pathogens, and so on. And that raises a question that has been challenging to answer: How does something as fundamental as a cell hold on to information across multiple divisions?

There's no one answer, and the details are really difficult to work out in many cases. But scientists have now worked out one memory system in detail. Cells are able to remember when their parent had a difficult time dividing—a problem that's often associated with DNA damage and cancer. And, if the problems are substantial enough, the two cells that result from a division will stop dividing themselves.

Setting a timer

In multicellular organisms, cell division is very carefully regulated. Uncontrolled division is the hallmark of cancers. But problems with the individual segments of division—things like copying DNA, repairing any damage, making sure each daughter cell gets the right number of chromosomes—can lead to mutations. So, the cell division process includes lots of checkpoints where the cell makes sure everything has worked properly.

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Antibodies are incredibly useful. Lots of recently developed drugs rely on antibodies that bind to and block the activity of specific proteins. They're also great research tools, allowing us to identify proteins within cells, purify both proteins and cells, and so on. Therapeutic antibodies have provided our first defenses against emerging viruses like Ebola and SARS-CoV-2.

But making antibodies can be a serious pain, because it involves getting animals to make antibodies for us. You need to purify the protein you want the antibodies to stick to, inject it into an animal, and get the animal will produce antibodies as part of an immune response. From there, you either purify the antibodies, or to purify the cells that produce them. It's time-consuming, doesn't always work, and sometimes produces antibodies with properties that you're not looking for.

But thanks to developments in AI-based protein predictions, all that hassle might become unnecessary. A recently developed diffusion model for protein structures has been adapted to antibody production and has successfully designed antibodies against flu virus proteins.

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Genetic mutations are essential for innovation and evolution, yet too many—or the wrong ones—can be fatal. So researchers at Cambridge established a synthetic “orthogonal” DNA replication system in E. coli that they can use as a risk-free way to generate and study such mutations. It is orthogonal because it is completely separate from the system that E. coli uses to copy its actual genome, which contains the genes E. coli needs to survive.

The genes in the orthogonal system are copied with an extraordinarily error-prone DNA replication enzyme, which spurs rapid evolution by generating many random mutations. This goes on while E. coli ’s genes are replicated by its normal high-fidelity DNA copying enzyme. The two enzymes work alongside each other, each doing their own thing but not interfering with the other’s genes.

Engineering rapid mutation

Such a cool idea, right? The scientists stole it from nature. Yeast already has a system like this, with a set of genes copied by a dedicated enzyme that doesn’t replicate the rest of the genome. But E. coli is much easier to work with than yeast, and its population can double in 20 minutes, so you can get a lot of rounds of replication and evolution done fast.

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There are many mysteries in life that we end up shrugging off. Why is urine yellow? It just is, right? Rather than flush that 125-year-old question down the toilet, scientists sought out the answer, discovering a previously unknown microbial enzyme was to blame.

The enzyme that has eluded us for so long is now known as bilirubin reductase. It was identified by researcher and assistant professor Brantley Hall of the University of Maryland, who was part of a team based at the university and the National Institutes of Health.

Bilirubin is an orange pigment released by red blood cells after they die. Gut microbes then use bilirubin reductase to break down bilirubin into colorless urobilinogen, which degrades into yellowish urobilin, giving urine that infamous hue. While urobilin previously had an association with the color of urine, the enzyme that starts the process by producing urobilinogen was unknown until now.

Enlarge / An ant carrying away one of the termites it preys on. (credit: Wikimedia Commons )

Although humans may think we are alone in creating antibiotics, there is a species of ant that secretes an especially powerful one—no pharma lab required.

The Matabele ants ( Megaponera analis) of sub-Saharan Africa eat only termites. Unfortunately, the fierce mandibles of termite soldiers cause injuries that, if infected, can turn fatal. Ants back at the nest rush to the injured and can tell which wounds are infected. They then secrete an antibiotic for them.

An international team of researchers observed these ants closely and analyzed their antibiotic secretion. They found it can reduce mortality by about 90 percent in injured ants and that the ants can identify chemical changes that result from infected wounds, focusing treatment on those that need it most.